CubeSats come in a range of standardised sizes. The basic "unit" is 10cm x 10cm x 10cm, but you can get CubeSats of 1 unit, 2, 3, 4, 6 units. The costs start at about $100,000 including launch.

There is (or was?) also company offering "TubeSats" which are tube-like, except that they have 16 flat sides for solar panels rather than being cylindrical. (Plus two ends, of course). They are about 3.5 inches diameter and 5 inches long, and the kit + launch costs only about $8,000. They are launched into a rapidly-decaying near Earth orbit, and probably only stay aloft for a few weeks. The payload can take up only about half of the interior space of the tube, the rest going on power supply, comms etc.